Interaction between phosphodiesterases in the regulation of the cardiac β-adrenergic pathway

Abstract

In cardiac myocytes, the second messenger cAMP is synthesized within the β-adrenergic signaling pathway upon sympathetic activation. It activates Protein Kinase A (PKA) mediated phosphorylation of multiple target proteins that are functionally critical to cardiac contractility. The dynamics of cAMP are also controlled indirectly by cGMP-mediated regulation of phosphodiesterase isoenzymes (PDEs). The nature of the interactions between cGMP and the PDEs, as well as between PDE isoforms, and how these ultimately transduce the cGMP signal to regulate cAMP remains unclear. To better understand this, we have developed mechanistically detailed models of PDEs 1–4, the primary cAMP-hydrolyzing PDEs in cardiac myocytes, and integrated them into a model of the β-adrenergic signaling pathway. The PDE models are based on experimental studies performed on purified PDEs which have demonstrated that cAMP and cGMP bind competitively to the cyclic nucleotide (cN)-binding domains of PDEs 1, 2, and 3, while PDE4 regulation occurs via PKA-mediated phosphorylation. Individual PDE models reproduce experimentally measured cAMP hydrolysis rates with dose-dependent cGMP regulation. The fully integrated model replicates experimentally observed whole-cell cAMP activation-response relationships and temporal dynamics upon varying degrees of β-adrenergic stimulation in cardiac myocytes. Simulations reveal that as a result of network interactions, reduction in the level of one PDE is partially compensated for by increased activation of others. PDE2 and PDE4 exert the strongest compensatory roles among all PDEs. In addition, PDE2 competes with other PDEs to bind and hydrolyze cAMP and is a strong regulator of PDE interactions. Finally, an increasing level of cGMP gradually out-competes cAMP for the catalytic sites of PDEs 1, 2, and 3, suppresses their cAMP hydrolysis rates, and results in amplified cAMP signaling. These results provide insights into how PDEs transduce cGMP signals to regulate cAMP and how PDE interactions affect cardiac β-adrenergic response.

Roles of phosphodiesterases in the regulation of the cardiac cyclic nucleotide cross-talk signaling network

“…In a previously developed model, we studied PDE regulation of cAMP and response of the β-adrenergic pathway by treating [cGMP] as a model parameter [39]. Here, we extend this model by incorporating a mechanistic description of cGMP production and degradation.…”

“…1B, cAMP degradation is regulated by PDEs 1–4 in cardiac myocytes [1, 4, 27, 32–36]. As a form of negative feedback, cAMP can stimulate its own degradation through activation of PDEs 2 and 4 (green arrows) [39]. The presence of cGMP can potentially increase cAMP concentration ([cAMP]) by inhibiting cAMP hydrolysis rates of PDEs 1 and 3 (red arrows) [39].…”

“…As a form of negative feedback, cAMP can stimulate its own degradation through activation of PDEs 2 and 4 (green arrows) [39]. The presence of cGMP can potentially increase cAMP concentration ([cAMP]) by inhibiting cAMP hydrolysis rates of PDEs 1 and 3 (red arrows) [39]. Depending on its concentration ([cGMP]), cGMP can either inhibit or potentiate [cAMP] by regulating PDE2 cAMP hydrolysis activity (alternating red/green arrows) [39].…”

“…The interpretation of experiments investigating the roles of multiple PDEs by measuring [cAMP] and/or [cGMP] in response to application of selective PDE inhibitors can be confounded by compensatory network interactions between the remaining PDEs [39]. As a result, it is difficult to attain a systems level understanding of the signaling network that bridges the causal link between the characteristics of individual signaling proteins and the collective response of the entire network.…”

Cross-regulation of Phosphodiesterase 1 and Phosphodiesterase 2 Activities Controls Dopamine-mediated Striatal α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Trafficking

“…Several examples of cyclic nucleotide control of PDE activity have been reported, such as allosteric regulation and competitive inhibition by cyclic nucleotide binding and phosphorylation by cyclic nucleotide-dependent kinases (16 -18). This leads to instances where cAMP levels can modulate the degradation of cGMP and vice versa, resulting in counterintuitive downstream responses (19,20). Furthermore, it is possible that, when PDEs are pharmacologically inhibited, these signaling features can result in the crossregulation of PDEs, meaning that the modulation of one PDE activity could affect the activity of an unintended second PDE regulated by cAMP/cGMP, causing unanticipated downstream signaling.…”